Research On Plasmon-enhanced Graphene-based Sensing

The optical diffraction limit greatly restricts the development and application of nanophotonic devices.Nano-devices based on plasmons have received widespread attention due to their ability to break through the diffraction limit to propagate and local field enhancement.By modulating the propagation of plasmons,the modulation of optical signals on the nanoscale can be achieved.Therefore,the design and research of sensors based on surface plasmons are the mainstream in the field of sensing.Among them,surface-enhanced Raman scattering(SERS)and surface plasmon resonance(SPR)of surface plasmons based on metal micro-nano structures have become extremely important branches.SERS is a technique that combines light-metal interaction and light-molecule interaction for the direct detection of surface molecules,SPR sensors are used for qualitative and quantitative detection by detecting the effect of target molecules on the metal surface on the resonance peaks of equilibrium excitons.So that,the plasmon exciton-based sensor techniques can reach single cell or even single molecule detection levels.On the other hand,since graphene was first prepared and obtained in 2004,graphene and graphene-based sensor have attracted great attention from many researchers in the theoretical and application exploration.It is well known that graphene,as the most representative two-dimensional(2D)material,has excellent properties such as large specific surface area and high carrier mobility,and is widely used to improve sensor performance.Based on the graphene-based plasmon sensor with simple operation and high sensitivity,this thesis conducts theoretical and experimental research on its plasma behavior.The main work is as follows:(1)A multilayer plasmon-enhanced SERS substrate was prepared based on graphene/silver nanoparticles,using graphene as a chemical mechanism layer(CM)and silver nanoparticles(Ag NPs)as an electromagnetic mechanism layer(EM)to form a CM-EM unit,build a multi-layer hybrid structure as a SERS substrate.The SERS performance of the improved multilayer nanostructures was studied experimentally and theoretically.We proved that the Raman enhancement effect increases with the increase of the number of CM-EM units.When the number of CM-EM units is greater than 4,the Raman enhancement effect hardly changes.The detection limit of rhodamine 6G(R6G)is 10^-14 M,and the detection limit of crystal violet(CV)is 10^-12M.Furthermore,the performance of graphene's oxidation resistance and excellent ductility has been exerted to achieve exciting thermal stability.(2)The SPR sensor is prepared based on graphene/silver film,and multimode plastic optical fiber(POF)is selected as the sensor platform,and the D-shaped area is the sensing area.The wavelength modulation type is used to construct the graphene-based SPR sensor to explore the sensing performance.Using the combination of graphene and silver metal nano-film,graphene excitons and metal plasma have a strong coupling effect,which improves the reliability and sensitivity of the SPR signal.By testing different concentrations of ethanol aqueous solution,good sensitivity(2546.8 nm/RIU)was obtained.Compared with pure silver nano-film,the sensitivity was increased by 2.3 times,which effectively proved the superiority of graphene-based sensors.